This invention relates to improved lightweight concretes of the type containing a cementitious hydratable binder and low-density particulate expanded vermiculite or perlite aggregate applied as wet layers to roof tops, etc.
Mixtures of hydratable cementitious binders such as Portland cement and expanded vermiculite aggregate are popularly employed in the formation of lightweight, low-density concretes having thermal insulating and fire-resisting properties. Such concretes are ideally suited for use in the construction of thermal insulating roofing system constructed at the job site. When mixed with water, the wet vermiculite-cementitious concrete mixtures can be mixed at ground level and pumped relatively long distances under relative high pressure to the roofs of buildings and the like without undesirable collapse of the porous structure of the expanded vermiculite aggregate or segregation of the components of the wet mixture during mixing and pumping. The inclusion of air-entraining surfactants in the mixes to aid pumpability and lower the density of the hardened product has been long practiced in the art. Expanded vermiculite-Portland cement insulating concretes of this type have been successfully used for some time in combination with lightweight cellular plastic thermal insulating boards, for example, expanded polystyrene boards, to construct exceptionally lightweight, high thermal-insulating, "built-up" roof systems. Examples of such roof systems wherein the concretes are poured in layers contiguous to such plastic insulating boards are shown in U.S. Pat. No. 3,619,961 to Sterrett et al. and U.S. Pat. No. 3,884,009 to Frohlich et al.
Insulating concretes containing porous highly water-absorptive expanded lightweight aggregate must be mixed with relatively large proportions of water in order to provide the wet mixture with sufficient fluidity to be pumped. Whereas typical water to cement ratios for structural Portland cement concretes (containing heavy, non-porous stone and sand aggregate) range between 0.4 to 0.7, a typical water to cement ratio for lightweight expanded vermiculite aggregate-containing concretes (containing the conventional 1 to 6, cement to vermiculite ratio by volume) ranges in excess of 2. The water in such lightweight concrete mixes is greatly in excess of that required to hydrate the cement component and its presence after placement and finishing of the concrete is undesirable. This has led in the past to the limited use of such insulating concretes in built-up roof systems of the aforementioned type over roof decks or roof substrates which had limited means of venting the excess moisture.
Lightweight thermal insulating concretes having relatively low water requirements are known in the art. Concretes based essentially upon mixtures of cement and expanded perlite aggregate (1:3 to 1:4 ratio by volume) and cement and expanded polystyrene beads (1:3 to 1:5 ratio by volume) are known. However, such perlite concretes may be abrasive and difficult to pump. The expanded polystyrene bead concretes tend to plug hoses during pumping, especially if the hose is restricted in any manner and also the expanded beads tend to float to the surface of the concrete. "Pregenerated foam" concretes having relatively low water demand are also known which are prepared by mixing cement with prepared "whipped" foams having the appearance of shaving cream. Such "pregenerated foam" concretes however suffer the disadvantage that the density thereof is very difficult to control.